matplotlib-users

[Matplotlib-users] basemap and fill_between()

[David C. <dcd...@gm...>]

Hi, I'm having a problem usinf fill_between() with basemap. I plot two
great circles and want to shade the region between them. My code is below,
it doesnt give any error just creates the plot without filling the area.
Does anyone know if it's possible to do this or should I try a different
method?
Thanks,
David

from mpl_toolkits.basemap import Basemap
from pylab import *

### PARAMETERS FOR MATPLOTLIB :
import matplotlib as mpl
rcParams['font.size'] = 10.
rcParams['font.family'] = 'Comic Sans MS'
rcParams['axes.labelsize'] = 8.
rcParams['xtick.labelsize'] = 6.
rcParams['ytick.labelsize'] = 6.

def shoot(lon, lat, azimuth, maxdist=None):
    """Shooter Function
    Original javascript on http://williams.best.vwh.net/gccalc.htm
    Translated to python by Thomas Lecocq
    """
    glat1 = lat * pi / 180.
    glon1 = lon * pi / 180.
    s = maxdist / 1.852
    faz = azimuth * pi / 180.

    EPS= 0.00000000005
    if ((abs(cos(glat1))<EPS) and not (abs(sin(faz))<EPS)):
        alert("Only N-S courses are meaningful, starting at a pole!")

    a=6378.13/1.852
    f=1/298.257223563
    r = 1 - f
    tu = r * tan(glat1)
    sf = sin(faz)
    cf = cos(faz)
    if (cf==0):
        b=0.
    else:
        b=2. * arctan2 (tu, cf)

    cu = 1. / sqrt(1 + tu * tu)
    su = tu * cu
    sa = cu * sf
    c2a = 1 - sa * sa
    x = 1. + sqrt(1. + c2a * (1. / (r * r) - 1.))
    x = (x - 2.) / x
    c = 1. - x
    c = (x * x / 4. + 1.) / c
    d = (0.375 * x * x - 1.) * x
    tu = s / (r * a * c)
    y = tu
    c = y + 1
    while (abs (y - c) > EPS):

        sy = sin(y)
        cy = cos(y)
        cz = cos(b + y)
        e = 2. * cz * cz - 1.
        c = y
        x = e * cy
        y = e + e - 1.
        y = (((sy * sy * 4. - 3.) * y * cz * d / 6. + x) *
              d / 4. - cz) * sy * d + tu

    b = cu * cy * cf - su * sy
    c = r * sqrt(sa * sa + b * b)
    d = su * cy + cu * sy * cf
    glat2 = (arctan2(d, c) + pi) % (2*pi) - pi
    c = cu * cy - su * sy * cf
    x = arctan2(sy * sf, c)
    c = ((-3. * c2a + 4.) * f + 4.) * c2a * f / 16.
    d = ((e * cy * c + cz) * sy * c + y) * sa
    glon2 = ((glon1 + x - (1. - c) * d * f + pi) % (2*pi)) - pi

    baz = (arctan2(sa, b) + pi) % (2 * pi)

    glon2 *= 180./pi
    glat2 *= 180./pi
    baz *= 180./pi

    return (glon2, glat2, baz)

#Create a basemap around N. Atlantic
m = Basemap(llcrnrlon=-45.0,llcrnrlat=30.0,urcrnrlon=15.0,urcrnrlat=75.0,
            resolution='i',projection='merc',lon_0=-17.5,lat_0=60.0)


m.drawcountries(linewidth=0.5)
m.drawcoastlines(linewidth=0.5)
m.bluemarble()
m.drawparallels(arange(40.,75.,10.),labels=[1,0,0,0],color='black',dashes=[1,0],labelstyle='+/-',linewidth=0.2)
# draw parallels
m.drawmeridians(arange(-45.,15.,10.),labels=[0,0,0,1],color='black',dashes=[1,0],labelstyle='+/-',linewidth=0.2)
# draw meridians

# Shade region defined by great circles.
x1, y1 = -9.1676613, 51.6029999
az1 = 270.
az2 = 290.
maxdist = 2000
x2, y2, baz = shoot(x1, y1, az1, maxdist)
x3, y3, baz = shoot(x1, y1, az2, maxdist)

m.drawgreatcircle(x1, y1, x2, y2, del_s=10, color='gray', lw=1.)
m.drawgreatcircle(x1, y1, x3, y3, del_s=10, color='gray', lw=1.)
a=linspace(x3,x1)
b=linspace(y2,y1)
c=linspace(y3,y1)
fill_between(a, b, c, where=None, alpha=0.2)
show()

Re: [Matplotlib-users] basemap and fill_between()

[Jerzy K. <jer...@un...>]

Le 13/05/2012 11:34, David Craig a écrit :
> Hi, I'm having a problem usinf fill_between() with basemap. I plot two 
> great circles and want to shade the region between them. My code is 
> below, it doesnt give any error just creates the plot without filling 
> the area. Does anyone know if it's possible to do this or should I try 
> a different method?
Hello, Boss.
Perhaps I am telling rubbish, but fill_between demands the coordinates 
within your axes, not the basemap angles. Your a,b,c contain some small 
numers (negative x, say -38) won't do any good, x should be, say 3001129 
etc. Use m(...) to convert.

Jerzy K

Re: [Matplotlib-users] basemap and fill_between()

[Jerzy K. <jer...@un...>]

Appendix.
(and excuses for my approximate syntax in the first message; I was doing 
three things simultaneously).

Maestro David Craig, your filling will be lousy anyway.
If your x and y arrays come from linespace, you will surely get a 
triangle, and not the curvilinear area between GreatCircles. You must 
transform the coordinates in a more clever (but equally easy...) way.

Jerzy K.

Re: [Matplotlib-users] basemap and fill_between()

[Jeff W. <js...@fa...>]

On 5/13/12 3:34 AM, David Craig wrote:
> Hi, I'm having a problem usinf fill_between() with basemap. I plot two 
> great circles and want to shade the region between them. My code is 
> below, it doesnt give any error just creates the plot without filling 
> the area. Does anyone know if it's possible to do this or should I try 
> a different method?
> Thanks,
> David
>

David Try replacing

m.drawgreatcircle(x1, y1, x2, y2, del_s=10, color='gray', lw=1.)
m.drawgreatcircle(x1, y1, x3, y3, del_s=10, color='gray', lw=1.)
a=linspace(x3,x1)
b=linspace(y2,y1)
c=linspace(y3,y1)
fill_between(a, b, c, where=None, alpha=0.2)

with

xx1,yy1 = m.gcpoints(x1,y1,x2,y2,100)
xx2,yy2 = m.gcpoints(x1,y1,x3,y3,100)
fill_between(xx1, yy1, yy2)

-Jeff


> from mpl_toolkits.basemap import Basemap
> from pylab import *
>
> ### PARAMETERS FOR MATPLOTLIB :
> import matplotlib as mpl
> rcParams['font.size'] = 10.
> rcParams['font.family'] = 'Comic Sans MS'
> rcParams['axes.labelsize'] = 8.
> rcParams['xtick.labelsize'] = 6.
> rcParams['ytick.labelsize'] = 6.
>
> def shoot(lon, lat, azimuth, maxdist=None):
>     """Shooter Function
>     Original javascript on http://williams.best.vwh.net/gccalc.htm
>     Translated to python by Thomas Lecocq
>     """
>     glat1 = lat * pi / 180.
>     glon1 = lon * pi / 180.
>     s = maxdist / 1.852
>     faz = azimuth * pi / 180.
>
>     EPS= 0.00000000005
>     if ((abs(cos(glat1))<EPS) and not (abs(sin(faz))<EPS)):
>         alert("Only N-S courses are meaningful, starting at a pole!")
>
>     a=6378.13/1.852
>     f=1/298.257223563
>     r = 1 - f
>     tu = r * tan(glat1)
>     sf = sin(faz)
>     cf = cos(faz)
>     if (cf==0):
>         b=0.
>     else:
>         b=2. * arctan2 (tu, cf)
>
>     cu = 1. / sqrt(1 + tu * tu)
>     su = tu * cu
>     sa = cu * sf
>     c2a = 1 - sa * sa
>     x = 1. + sqrt(1. + c2a * (1. / (r * r) - 1.))
>     x = (x - 2.) / x
>     c = 1. - x
>     c = (x * x / 4. + 1.) / c
>     d = (0.375 * x * x - 1.) * x
>     tu = s / (r * a * c)
>     y = tu
>     c = y + 1
>     while (abs (y - c) > EPS):
>
>         sy = sin(y)
>         cy = cos(y)
>         cz = cos(b + y)
>         e = 2. * cz * cz - 1.
>         c = y
>         x = e * cy
>         y = e + e - 1.
>         y = (((sy * sy * 4. - 3.) * y * cz * d / 6. + x) *
>               d / 4. - cz) * sy * d + tu
>
>     b = cu * cy * cf - su * sy
>     c = r * sqrt(sa * sa + b * b)
>     d = su * cy + cu * sy * cf
>     glat2 = (arctan2(d, c) + pi) % (2*pi) - pi
>     c = cu * cy - su * sy * cf
>     x = arctan2(sy * sf, c)
>     c = ((-3. * c2a + 4.) * f + 4.) * c2a * f / 16.
>     d = ((e * cy * c + cz) * sy * c + y) * sa
>     glon2 = ((glon1 + x - (1. - c) * d * f + pi) % (2*pi)) - pi
>
>     baz = (arctan2(sa, b) + pi) % (2 * pi)
>
>     glon2 *= 180./pi
>     glat2 *= 180./pi
>     baz *= 180./pi
>
>     return (glon2, glat2, baz)
>
> #Create a basemap around N. Atlantic
> m = Basemap(llcrnrlon=-45.0,llcrnrlat=30.0,urcrnrlon=15.0,urcrnrlat=75.0,
>             resolution='i',projection='merc',lon_0=-17.5,lat_0=60.0)
>
>
> m.drawcountries(linewidth=0.5)
> m.drawcoastlines(linewidth=0.5)
> m.bluemarble()
> m.drawparallels(arange(40.,75.,10.),labels=[1,0,0,0],color='black',dashes=[1,0],labelstyle='+/-',linewidth=0.2) 
> # draw parallels
> m.drawmeridians(arange(-45.,15.,10.),labels=[0,0,0,1],color='black',dashes=[1,0],labelstyle='+/-',linewidth=0.2) 
> # draw meridians
>
> # Shade region defined by great circles.
> x1, y1 = -9.1676613, 51.6029999
> az1 = 270.
> az2 = 290.
> maxdist = 2000
> x2, y2, baz = shoot(x1, y1, az1, maxdist)
> x3, y3, baz = shoot(x1, y1, az2, maxdist)
>
> m.drawgreatcircle(x1, y1, x2, y2, del_s=10, color='gray', lw=1.)
> m.drawgreatcircle(x1, y1, x3, y3, del_s=10, color='gray', lw=1.)
> a=linspace(x3,x1)
> b=linspace(y2,y1)
> c=linspace(y3,y1)
> fill_between(a, b, c, where=None, alpha=0.2)
> show()
>
>
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